Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains Thomas Gnäupel-Herold1,2

Uniaxial and Multiaxial Plastic Deformation of Large Niobium Grains

• Thomas Gnäupel-Herold1,2,

• Adam Creuziger, T.Foecke3

• 1University of Maryland

• 2NIST Center for Neutron Research

• 3NIST Metallurgy Division

Formability: strain localization on grain boundaries

Tensile Tests Orientations

Tensile Tests

Yield Stress

• YS between 25 MPa and 40 MPa

• weak anisotropy

• 25% YS of poly-crystal

R-Values

• Extreme anisotropy from r=0 (thinning only) to r>1 (no thinning)

• Polycrystal r=0.1

• Large r-values for {210}<-120>

Effect of Annealing

Sample prep for multiaxial tests

Multi-axial Testing

A - Uniaxial Test

B - Uniaxial Test, 90 deg rotated

C - Balanced Biaxial Test

D - Plane Strain

E - Plane Strain, 90 deg. rotated

E – Plane Strain

EBSD: Misorientations at the tri-junction

Analysis of present data

• What is known ….

• Full strain rate tensor at every point on the sample and in time

• orientations

Taylor’s model

• Imposed strain rate tensor

• Write the strain rate tensor as a combination of all the slip systems

Conclusions

• 5 Multi-axial straining tests of tri-crystal plates with identical orientation performed

• Local strain rate data collected

• Orientation analysis with EBSD

• GOAL: determination of locally active slip systems for any given moment